The overall goal of this project is to provide basic biomechanical information about the knee that can be used to improve the treatment of osteoarthritis and increase the longevity of total knee arthroplasty while restoring closer- to-normal patient function. Problems related to polyethylene wear are among the major factors relating to mechanical failure of total knee arthroplasty. An important facet of this problem is understanding the functional role of the posterior cruciate ligament (PCL), since retention or removal of this ligament plays a major role in the selection of the appropriate shape of the articulating surfaces. This study addresses the problem from a new viewpoint, which is the dynamic interaction between the PCL and quadriceps function. The first Specific Aim of this proposal tests the hypothesis that quadriceps contraction at knee flexion angles greater than approximately 45 degrees will produce a significantly greater displacement of the femur on the tibia than knees without a PCL. This hypothesis will be tested in a group of patients with PCL-deficient knees using a new Step-Test, where precise relative movement of the femur on the tibia will be measured. In addition, subjects will be tested in standard protocols of level walking, stairclimbing, and rising from a seated position. The second hypothesis tests the premise that if PCL function is restored or substituted for appropriately by total knee replacement, normal function can be achieved during more stressful activities such as stairclimbing. A prospective randomized study of patients who are candidates for total knee replacement will be conducted, where patients will be assigned either a design that retains, or substitutes for, the PCL. The patients will be tested in both the Step-Test protocol and the Functional Testing Protocol. The information generated from these studies is intended to provide new information on the dynamic interaction between passive soft tissue (PCL) and active muscle contraction during specific activities. It is suggested that this information will be extremely useful in evaluating patient function, as well as understanding the biomechanics of total knee arthroplasty.